JPH02689Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal level measuring circuit that is capable of measuring minute monitor signals that are output in the form of pulses with an ammeter.

Conventionally, monitor output circuits provided to know the operating status of circuits with low current consumption have generally been configured to have high output impedance to prevent increases in the current consumption of the circuit. Therefore, to measure the monitor output, you typically connect a high-input impedance measuring device in parallel to the monitor output impedance to measure the voltage, or connect a low-impedance ammeter in series with the monitor output impedance to measure the current. I try to do this.

By the way, when the monitor output is a pulse-like minute signal, a memory scope or peak voltmeter is used to measure the voltage mentioned above.
When measuring equipment installed in the field, it is difficult to carry the measuring equipment, and even if you try to measure the monitor output with an ammeter range of a tester that is easy to carry instead of these measuring equipment, the circuit is too low. Because it consumes current, the current that can be taken out from the monitor circuit is extremely small, so it cannot be used unless the meter sensitivity is good.Moreover, ammeters have difficulty responding to pulsed signals, so stable measurement of monitor signals is difficult. The problem is that it is difficult. In addition, a sample and hold circuit is used to receive and hold pulse signals, but in this case, the current consumption of the sample and hold circuit cannot be ignored, so for example,
It is inappropriate as a monitor circuit for a circuit designed with a current consumption of about 10 mA.

This invention was developed in view of the above problems, and is mainly used as a monitor output circuit that can output stable measurable pulse-like signals using the ammeter range of a general tester. The purpose of the present invention is to provide a level measuring circuit for minute signals with low power consumption.

Hereinafter, the present invention will be explained based on the drawings.

Figure 1 shows a separate photoelectric smoke detector that generates a pulse-like minute monitor signal using a level measuring circuit according to the present invention, where 1 is a power supply circuit, 2 is an oscillation circuit, and 3 is an oscillation circuit. 2 is a light emitter that is activated to emit pulsed light; 4 is a light receiver that receives attenuated light due to smoke of the pulsed light emitted from the light emitter 3 at a predetermined distance and converts it into an electrical signal; 5;
6 is an amplifier circuit that amplifies the received light output; 6 is an output peak hold circuit that takes the peak value of the received light amplified output; 7 is an output peak hold circuit that takes the peak value of the received light amplified output;
is a fire determination circuit that outputs an alarm signal when the received light output exceeds a predetermined value. In such a photoelectric smoke detector, in order to align the optical axis between the light emitter 3 and the light receiver 4, a monitor circuit 8 is provided to monitor the pulsed light reception output obtained via the peak hold circuit 6. As this monitor circuit 8,
By using the level measuring circuit according to the present invention, the level of the pulsed light receiving output can be measured with an ammeter 9 such as a tester.

FIG. 2 is a circuit diagram showing an embodiment of the present invention. First, to explain the configuration, input terminals 10, 1
It has a first switch circuit 13 that opens and closes so as to apply an input signal to the gate G of the N-channel type MOS-FET 12 when a pulse signal is applied between 0' and 0'. The first capacitor C ₁ stores its level by being charged and discharged by the input signal added when the switch circuit 13 is closed.
A second capacitor C ₂ is connected in parallel with this capacitor C ₁ and stores its level by charging and discharging according to the input signal when the first switch circuit 13 is closed. The second switch circuit 14 is connected in series with the second switch circuit 14.

The second switch circuit 14 is a third switch circuit that operates for a predetermined time so as to add the reference voltage V _Z generated by the reference voltage source consisting of the resistor R ₂ and the Zener diode ZD to the level stored in the capacitor C ₂ . 15 are connected in parallel, and this third switch circuit 15 connects the first and second switch circuits 1
3 and 14 are opened and closed in the opposite manner. That is, when the first and second switch circuits 13, 14 are closed, the third switch circuit 15 is open, and conversely, when the switch circuits 13, 14 are open, the switch circuit 15 is closed for a predetermined period of time. become. Note that a resistor may be used instead of the Zener diode ZD.

Resistor connected between input terminals 10 and 10'
_R1 is a resistor for forming a path for discharging the capacitors _C1 and _C2 when the input signal is lower than the charge level of the capacitors _C1 and _C2 .

The MOS-FET 12 is gate-biased by the voltage of the capacitor _C1 to control the drain current _ID , and an ammeter 9 is connected to the source S side via a current-limiting resistor _R3 .

Here, the reason why a depletion type N-channel type is used for MOS-FET 12 is that, as shown in Fig. 3, the _drain This is because the characteristic is that the current _ID increases, so the output current can be increased in response to an increase in the input level. On the other hand, P-channel type MOS
If a −FET is used, the drain current will decrease as the input level increases, which makes it difficult to measure the input signal level, so an N-channel MOS-FET is used. It is something to do.

Next, referring to the time chart in Figure 4,
The operation of the illustrated embodiment will be explained.

Now, if a pulse input is applied between the input terminals 10 and 10' at time _t1 , then each of the switch circuits 13 and 14 is closed, and each of the capacitors _C1 and _C2 is closed depending on the magnitude of the input signal. and memorize the signal level. At this time, switch 15 is open.

In this way, the level of the input signal is
When stored in C ₁ and C ₂ , switch circuits 13 and 14 open at subsequent time t' ₁ , and at the same time switch circuit 1
5 is closed for a predetermined time, and the Zener diode ZD is connected in series to the capacitor C ₂ via the switch circuit 15, so that the voltage on the gate G side of the capacitor C ₂ is equal to the storage level V _C of the input signal and the reference voltage V _Z
This voltage is the sum of the voltage (V _C + V _Z )
charges the capacitor _C1 .

Looking at the operation of MOS-FET12 at this time,
Between times t ₁ and t' ₁ , addition by the reference voltage V _Z is not performed, so the I _D -V _GS characteristic is curve A shown in Figure 3, but at time t' ₁ By superimposing the reference voltage V _Z , the I _D -V _GS characteristic is shifted up as shown by curve B. In other words, as is clear from curve A in Figure 3, in a depletion type N-channel MOS FET, when the input voltage _VGS applied between the gate and source is approximately 1.5V or less, the drain current is less than 0.0001mA. , cannot be measured with a general tester's ammeter, but for example, approx.
When adding the reference voltage V _Z of 1.5 V, the input voltage V _GS applied between the gate and source is approximately
0.001mA, or about 1μA, flows,
For example, if you use the 50μA range of a typical tester, you can visually read current fluctuations of this magnitude.

Therefore, in the absence of the reference voltage V _Z , if the input signal was approximately 1.5 V or less, it would be almost impossible to measure even if a tester was used as a monitor circuit, but by adding the reference voltage V _Z of the present invention. This allows measurement even if the input signal is zero.

The signal voltage superimposed on the reference voltage V _Z due to the closure of the switch circuit 15 is transferred to the capacitor C ₁
Since the potential of the capacitor C1 is also charged at the same level, and the switch circuits 13 and 14 are open, and the switch circuit 15 is also opened after a predetermined time, there is no discharge route for the capacitor _C1 , and therefore the next input signal is applied. time t ₂
At time _t2 , the switch circuits 13 and 14 are closed again, and the signal level at that time is stored in the capacitors _C1 and _C2 again, and at time _t'2 , the switch circuits 13 and 14 are opened. Then, the switch circuit 15 is closed for a predetermined period of time, and the reference voltage V _Z is superimposed and held. Thereafter, similarly, the above operation is repeated every time a pulse signal is applied.

Here, the signal level is stored in the capacitors C ₁ and C ₂ until the time when the next input signal is applied.
The reason for this is that when a tester is used as a monitor circuit, the tester generally slows down the response speed of the meter needle to prevent sudden contact with the meter needle, and the meter needle cannot be read visually. In order to do this, it is necessary to stop the meter needle for a specified period of time.
Therefore, by storing the signal level of the previous input signal using the capacitors C ₁ and C ₂ , accurate reading by the tester becomes possible.

In the time chart of FIG. 4, the timing for opening and closing the switch circuits 13, 14, and 15 is synchronized with the input signal, but when the switch circuits 13, 14 are closed, the input signal is applied. It is sufficient that the switch circuit 1
3 and 14 are closed, the capacitor C ₁ ,
Determined by the charge/discharge time constant of C ₂ .

A means for controlling the opening and closing of the switch circuits 13, 14, and 15 can be easily realized using, for example, a monostable multivibrator that generates a pulse with a predetermined time width in synchronization with the rising edge of an input signal, or a counter. I can do it.

FIG. 5 shows another embodiment of the present invention.
This device is characterized by a switch circuit 16 that opens and closes in conjunction with the switch circuit 15 in series with the resistor R ₂ that generates the reference voltage V _Z and the Zener diode ZD, and the other configuration is the same as that shown in FIG. Same as example.

When the switch circuit 16 is provided in this way, the second
In the example shown in the figure, the Zener diode ZD, which is always conductive and generates the reference voltage V _Z , is now connected to the reference voltage V _Z
Since the switch circuit 15, which requires a switch, becomes conductive only when it is closed, the current consumption of the circuit can be further reduced.

The above embodiment was applied to a monitor circuit for a separate photoelectric smoke detector, but the level measurement circuit of the present invention is suitable for pulse-type smoke detectors that are difficult to measure with an ammeter. It can be applied to various types of equipment that require a signal measurement circuit.

As explained above, according to the present invention, the configuration is such that the peak level of the input voltage applied to the gate of the N-channel MOS-FET is once memorized using a capacitor, and after being memorized, a reference voltage is superimposed and applied to the gate. Since the voltage is applied and held for a certain period of time,
Even a minute pulse signal can be extracted as a continuous measurement output according to the level of the input signal that can be read on the ammeter range of a general tester, and when used as a monitor output circuit, Measurements can be made while installed on site using simple measuring instruments such as testers.
It is possible to obtain the effects that operations such as maintenance inspection and adjustment become easier, and stable measurements can be performed.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of a separate photoelectric smoke detector using the measurement circuit of the present invention.
Figure 2 is a circuit diagram showing an embodiment of the present invention;
The figure shows an N-channel type used in the embodiment shown in Figure 2.
A graph showing the I _D -V _GS characteristics of MOS-FET, Fig. 4 is a time chart showing the operation of the embodiment of Fig. 2, and Fig. 5 is a circuit showing another embodiment of the present invention. It is a diagram. DESCRIPTION OF SYMBOLS 1... Power supply circuit, 2... Oscillation circuit, 3... Light emitter, 4... Light receiver, 5... Amplifier, 6... Peak hold circuit, 7... Fire determination circuit, 8... Monitor circuit, 9 ...Ammeter, 10,10'...Input terminal, 12...N channel MOS-FET, 13,
14, 15, 16... switch circuit, R ₁ to R ₃ ...
...Resistor, C ₁ , C ₂ ... Capacitor, ZD ... Zener diode.

Claims (1)

[Claims for Utility Model Registration] When the input signal is applied, the N-channel type
a first switch circuit that opens and closes so as to apply the input signal to the gate of the MOS-FET; and a first switch circuit that is connected to the gate of the MOS-FET and stores the level of the input signal that is applied when the first switch is closed. When a capacitor No. 1 and a second switch circuit connected in parallel to the first capacitor and opened and closed in conjunction with the first switch circuit are closed, an input is applied through the first switch circuit. 2nd to memorize the signal level
After storing the input signal level in the first and second capacitors, a predetermined reference voltage generated by a reference voltage source is added to the stored level of the second capacitor, and the input signal level is transferred to the first capacitor. and a third switch circuit that closes when the first and second switch circuits are opened so as to store the signal level.